1. Field of the Invention
The present invention relates to a data processing apparatus and a method for use with the apparatus, and is preferably applied to a decoding device which outputs video and audio by decoding compressed video data and compressed audio data encoded according to, for example, the Moving Picture Experts Group Layer 2 (MPEG2) system, etc.
2. Description of the Related Art
Recently, a digital broadcast receiver has become widespread as a decoding device of the above-mentioned type. The digital broadcast receiver is configured to output video and audio according to a procedure RT1X as shown in FIG. 1 when, for example, a user performs a channel switching operation.
That is, the digital broadcast receiver passes control to step SP1 when a user performs a channel switching operation, and receives a Network Information Table (NIT). The NIT contains physical information about a transmission line (in this case, an orbit of a satellite, a polarized wave, a frequency for each transponder, etc.). Thus, the digital broadcast receiver can select a transponder corresponding to a request channel requested in the channel switching operation based on the NIT, and as a result receive a transport stream corresponding to the request channel.
Then, the digital broadcast receiver passes control to step SP2, and receives a Program Association Table (PAT). The digital broadcast receiver then passes control to step SP3, and receives a Program Map Table (PMT) corresponding to the request channel based on the PAT.
Then, the digital broadcast receiver passes control to step SP4, and realizes a Program Identification (PID) corresponding to the request channel based on such PMT. In this case, the PID corresponds to the identification information for identifying a packet containing the compressed video data, compressed audio data, Program Clock Reference (PCR) data, etc. corresponding to the request channel. The digital broadcast receiver can obtain the compressed video data, compressed audio data, PCR data, etc. corresponding to the request channel as a stream by separating a packet corresponding to the recognized PID from a received transport stream.
The processes in step SP1 to SP4 described above are well known as a DEMUX process (refer to Japanese Patent Application JP2003-274304).
The obtained PCR data in the stream includes the system time clock at an encoding device which encodes the compressed video data and the compressed audio data.
Therefore, when the digital broadcast receiver passes control to the next step SP5, it sets the System Time Clock (STC) kept in the digital broadcast receiver to the time clock kept in the PCR data. Thus, the system time clock kept by the digital broadcast receiver can be synchronized with the time clock kept at the encoding device.
Also in the stream, as shown in FIG. 2, the Presentation Time Stamp (PTS) indicating the time when the video is to be presented is associated with each piece of video data “Dpic (0)”, “Dpic (1)”, . . . corresponding to one frame for example. Likewise, in the stream, the sounding time stamp (PTS) indicating the time when the audio is to be outputted is associated with each piece of compressed audio data “Dframe (0)”, “Dframe (1)”, . . . corresponding to one frame for example.
Thus, the digital broadcast receiver passes control to step SP6, for example, when the kept system time clock matches the presentation time stamp “pts (0)” associated with the compressed video data “Dpic (0)”, and presents on the presentation device the video “Vpic (0)” based on the video data obtained by decoding the compressed video data “Dpic (0)”.
In addition, the digital broadcast receiver passes control to step SP7 when the kept system time clock matches the sounding time stamp “pts (0)” associated with the compressed audio data “Dframe (0)”, and outputs the audio “Sframe (0)” based on the audio data obtained by decoding the compressed audio data “Dframe (0)” through a speaker, etc.
Thus, the digital broadcast receiver can allow to some extent the video presentation timing indicating the video “Vpic (0)”, . . . to match the sounding time outputting the audio “Sframe (0)”, . . . corresponding to the video “Vpic (0)”.